An equally valid question is why not? The influence of the Roman Catholic church in the daily lives of Quebecers was pronounced to say the least till the Duplessis years roughly, when it began to wane. I see nothing special at all in the choice. Place names Saint-this and Notre-Dame-that are strewn all over the place, and dit names could just as readily reflect geography as profession etc...
But knowing his specific rationale would be priceless in terms of family history, The dit name of my family stopped in my branch at dad's baptism, and not used by him in any formal proceeding thereafter ttbomk. His generation generally saw the last of it.